The present invention relates generally to an apparatus for increasing the dissolved oxygen concentration in flowing water for efficient raising of fish on a commercial scale where there is multiple use of water in a series of ponds or reservoirs. More specifically, the present invention relates to the utilization of the kinetic energy of falling water to rotate a bristle brush and break the stream of water into small droplets thereby increasing the water surface area and allowing increased absorption of atmospheric oxygen.
Fish farming and other types of aquaculture on a large, commercial basis have become an important source of food and other products for human consumption and is a rapidly growing industry. In the breeding and raising of various types of fish, rainbow trout for example, it is critical to the success of the operation that the fish are properly cared for including supplying sufficient levels of dissolved oxygen in the water that the fish are raised in. It is well-known that the number of fish that a pond or reservoir can support and the overall condition of the fish may be substantially increased by providing aeration of the pond water.
There are four basic types of aeration systems in use today: (1) gravity, (2) surface, (3) diffuser and (4) turbine. Each type operates on the principle of increasing the liquid surface area available for oxygen absorption and/or mixing the liquid to ensure that water of low oxygen concentration is brought in contact with air or oxygen gas. U.S. Pat. No. 3,747,904 entitled, "Apparatus for Aerating Water" granted to William R. Gross on July 24, 1973 discloses a paddle wheel including a plurality of air-gathering buckets partially immersed in the water and rotated to create an artificial current and to aerate the water. The paddle wheel of Gross provides mixing of the water and a greater surface area by agitation of the pond surface. Atmospheric air is also introduced into the pond water to provide increased absorption of atmospheric oxygen in the water.
Typically, rainbow trout are raised in ponds having a flow-through of water; i.e., the water will enter the pond at an upper or upstream end and exit the pond at a lower or downstream end. In order to allow multiple use of the water, the ponds will typically be arranged in a series (raceway) such that the water flows from a first, upper pond into a second, lower pond. Such systems may include as many as eight ponds, each pond lower in elevation than the preceding pond. Since the water level in the various ponds in such an aquaculture system is often controlled by small dams or weirs, water falling over the top of a weir is a common aerator design used to replenish the dissolved oxygen level in the water as the water passes from one pond to the next pond in the system. As the water falls over the weir it breaks up into droplets substantially increasing the water surface area. Additionally, the water passing over a weir creates turbulence as it falls into the pond below providing mixing and aeration of the pond water.
While waterfalls are very effective aerators, modifications such as splash boards provide substantially increased efficiency. Chesness and Stephens, in an article entitled "A Model Study of Gravity Flow Aerators for Catfish Raceway System" published in the Transactions of the ASAE (1971), studied several gravity aerator designs including a weir with a rotating brush. The rotating brush was mounted at the foot of the weir partially immersed in the water and positioned and supported in such a manner that the falling water passing over the weir impacted the upstream side of the brush, causing rotation of the brush toward the headwall. The depth of immersion into the pond was chosen to provide maximum turbulence of the pond water.